Thursday, December 24, 2015

Magnetic field lines (purple) are twisted as they are dragged inward toward a swirling, dusty disk surrounding a young star in this artist's conception. Credit: Bill Saxton, NRAO/AUI/NSF.

Using new images that show unprecedented detail, scientists have found
that material rotating around a very young protostar probably has
dragged in and twisted magnetic fields from the larger area surrounding
the star. The discovery, made with the National Science Foundation's
Karl G. Jansky Very Large Array (VLA) radio telescope, has important
implications for how dusty disks -- the raw material for planet
formation -- grow around young stars.

The scientists studied a
young protostar about 750 light-years from Earth in the constellation
Perseus. Their observations, made in 2013 and 2014, measured the
alignment, or polarization, of radio waves emitted by material, mostly
dust, falling into a burgeoning disk orbiting the young star. The
polarization information revealed the configuration of magnetic fields
in this region near the star.

"The alignment of magnetic fields
in this region near young stars is very important to the development of
the disks that orbit them. Depending on its alignment, the magnetic
field can either hinder the growth of the disk or help funnel material
onto the disk, allowing it to grow," said Leslie Looney, of the
University of Illinois at Urbana-Champaign.

As material from the
envelope of dust and gas surrounding the young star falls inward toward
the rotating disk, it is likely to drag magnetic field lines with it.
Because of this, the structure of the magnetic field near the star will
become different from the field's structure farther away.

"Our
VLA observations are showing us this region, where the change in shape
of the magnetic field is taking place," said Erin Cox, also of the
University of Illinois Urbana-Champaign. The observations, she added,
produced the first images at wavelengths of 8 and 10 millimeters to show
the polarization near a protostar.

The observations also
indicated that millimeter- to centimeter-sized particles are numerous in
the disk surrounding the young star. Since the protostar is only about
10,000 years old -- very short in astronomical timescales -- this may
mean that such grains form and grow quickly in the environment of a
still-forming star.

The star, dubbed NGC1333 IRAS 4A, is one of
two young stars forming within a common envelope of dust and gas. The
disk around it contains material with a total mass more than twice that
of our Sun.

Cox and Looney are part of an international team of
astronomers studying the protostar. The scientists are reporting their
results in the Astrophysical Journal Letters.

The
National Radio Astronomy Observatory is a facility of the National
Science Foundation, operated under cooperative agreement by Associated
Universities, Inc.